Method of applying a protective coating to a metallic structure



I... R. ERWIN ETAL A ril 18, 1967 METHOD OF APPLYING A PROTECTIVE COATING TO A METALLIC STRUCTURE Original Filed Feb. 21, 1961 INVENTOR. LEE R. ERWIN DOUGLAS W. MC CALLUM RALPH H. GIESER BY ATTORNEY.

United States Patent 3,314,815 METHOD OF APPLYING A PROTECTIVE COAT- ING TO A METALLIC STRUCTURE Lee R. Erwin, Duarte, Douglas W. McCallum, Hacienda Heights, and Ralph H. Gieser, La Habra, Califi, assignors to Carrier Corporation, Syracuse, N.Y., a corporation of Delaware ontinuation of application Ser. No. 90,844, Feb. 21, 1961. This application Oct. 25, 1963, Ser. No. 319,046 1 Claim. (Cl. 117-40) This application is a continuation of our co-pending applicationSer. No. 90,844, filed on Feb. 21, 1961 and now abandoned.

This invention relates broadly to the art of providing a surface of a structural unit with a coating of a material to protect the surface. More particularly, this invention relates to a method of applying a coating of porcelain enamel to a structural unit. Still invention relates to a method of porcelain enamel to to be coated has, by its design, tion.

In the manufacture of domestic hot water heating units it has been long recognized that the surface of the tank assembly employed in the unit be provided with a lining of porcelain enamel in order that the useful life of the tank be prolonged. The porcelain enamel coating applied to the inner surface of the tank forms What is commercialy known as a glass-lined hot Water heating unit. The porcelain enamel lining serves as a protective coating for the material forming the tank or water accommodating unit. Usually,

either sheet there is presented porcelain enamel applicator means, a surface FIGURE 1 is a view in section showing a tank assembly of the type used in the fabrication of a domestic hot water heating unit and which contains a surface configuration of the kind with which the invention may be used.

FIGURE 2 is an enlarged fragmentary view showing in section the connection between two of the elements illustrated in FIGURE 1.

FIGURE 3 is a somewhat schematic view of a structural connected parts with at least one coating of porcelain enamel. The final assembly is completed by coating one surface ted from the drawing.

In the construction under consideration here, the end cover and cylindrical shell members 10 and 11, are connected by'causing terminal portions 12 and 13, respectively, of the two parts to be overlapped and indicated at 14. The inner surface thus presented for unit in the region of the connection between the surfaces 16 and 17.

thereof. This equipment is conventional in the art and it is felt that no further explanation The invention herein contemplated involves supplying heat to that portion of the welded unit wherein the unevenness in the surface configuration exists prior to and the porcelain enamel slip is applied to the surface thereof. To this end, a burner the conveyor so that it may heat the portion of the structural unit wherein the connection between the head and shell members is located. The operation of the burner is such that upon arrival of the unit at the spraying station the burner is energized and heat is applied immediately to the region referred to above. The supply of heat is continued during the period in which the spray head extends into and is retracted from the interior of the shell and cover assembly.

By preheating the region of the tank parts in the manner described, a portion of the surface having a temperature in excess of the remainder of the unit is provide-d. Once the porcelain enamel slip is sprayed onto that region, vaporization of the vehicle occurs such as will decrease the viscosity of the slip and make it less prone to flow away from the area defined by the surface 18 and the adjoining portions of the surfaces 16 and 17. Once the heat is continued, the porcelain enamel slip is further dried and partially sets so that if it is desired to add a second coating to the first coat prior to firing the porcelain enamel, the spraying action of the second coat will not cause the portions of the first coat in the vicinity of the connection to be pitted or washed away.

While the degree of heat does not appear to be critical it is recommended that the temperature be maintained short of causing the moisture in the porcelain enamel slip to boil, which, of course, would cause the porcelain enamel to tend to separate from the surface. On the other hand, the temperature should be high enough so that there is a tendency for the water in the porcelain enamel slip to vaporize and cause the resulting mixture to be more viscous.

While we have described and illustrated a preferred embodiment of our invention, it will be understood our invention is not limited thereto since it may be otherwise embodied within the scope of the following claim.

We claim:

In a method of applying a coating of porcelain enamel to a surface of a structural unit wherein said surface includes angularly related portions presenting an irregular configuration, which comprises the steps of preheating the outer surface of the structural unit in the region of said irregular configuration prior to the application of a porcelain enamel slip to the inner surface of said region, and continuing to heat said unit in the region of said irregular configuration while applying a coating of porcelain enamel in slip form so that the vehicle content of said slip is partially evaporated thus providing a coating of relatively dry porcelain enamel on said inner surface of said structural unit in the region of said irregular configuration.

References Cited by the Examiner UNITED STATES PATENTS ALFRED L. LEAVITT, Primary Examiner. RICHARD D. NEVIUS, Examiner. W. L. JARVIS, Assistant Examiner. 

